1. Field of the Invention
The present invention relates to a reflective mask, a manufacturing method for the reflective mask, and a manufacturing method for a semiconductor device.
2. Description of the Related Art
Extreme ultraviolet (EUV) lithography is an exposure method in which light (an X ray) having extremely short wavelength near 13.5 nanometers is used. The EUV lithography is prospective as a method of forming a finer pattern on a wafer than that formed by light exposure in the past (having wavelength of 193 manometers (ArF) or 248 nanometers (KrF).
The pattern formed on the wafer by the EUV lithography is, for example, a pattern smaller than 50 nanometers. Therefore, a technical level required for defect inspection and defect correction for a mask for forming a pattern to be transferred onto the wafer is high. For example, to form a pattern having width of 32 nanometers on the wafer using a 4X mask, it is necessary to form a pattern having width of 128 nanometers on the mask. To keep fluctuation in a pattern dimension on the wafer within 5%, it is necessary to keep dimension fluctuation of a mask pattern within 6.4 nanometers. Therefore, it is necessary to perform inspection of the mask pattern at accuracy of a dimension equal to or smaller than 6.4 nanometers. When a pattern finer than 32 nanometers is formed on the wafer, it is necessary to inspect the mask pattern in specifications stricter than 6.4 nanometers.
In the past, a reflective mask used for EUV exposure and the like is manufactured by arranging an EUV light absorber (a Ta compound, etc.) on a mask and etching the absorber according to a pattern to be exposed. In such a reflective mask, a buffer layer formed of Cr, a Cr compound such as CrN, or the like is arranged below an absorber layer as an etching stop layer (see, for example, Japanese Patent Application Laid-Open No. 2006-13494). The buffer layer is necessary for obtaining signal contrast with the absorber not only during the etching of the absorber but also during inspection of a mask pattern by an electron microscope. During mask pattern formation, the buffer layer is present over the entire mask between the absorber and a Mo/Si multilayer film for reflecting EUV light. Such a buffer layer causes deterioration in the intensity of reflected light. Therefore, after formation of an absorber pattern, a section without the absorber is etched and removed to expose the Mo/Si multilayer.
However, in the technology in the past, the inspection of the mask pattern is performed before the etching and removal of the buffer layer, i.e., the etching and removal of the buffer layer is performed after the inspection. Therefore, a defect that occurs in this etching process is not inspected. Examples of the defect that occurs in the etching process for the buffer layer include a partial (local) etching removal residue of a buffer layer material and a pattern dimension change due to redeposit of the removed buffer layer material on the absorber pattern. Therefore, a pattern is formed on the wafer by the mask in which the defect occurs. As a result, a pattern cannot be formed on the wafer in a desired dimension.